Search lights are used in a number of applications including vehicle headlights, underwater lights, search lights for emergency vehicles such as police cars, helicopters, etc., and the like. In many of these applications, it is desired to provide a narrow beam of light. A narrow beam of light may be desired to provide more effective illumination at large distances, greater intensity for a given light source at a given distance and to reduce the intensity of stray light outside of the desired area of illumination that may, for example, annoy oncoming motorists or pose a safety risk.
Search lights typically include a light source, a reflector behind the light source and a lens in front of the light source. The reflector and lens are intended to act in concert to collect light from the source and collimate or focus the light into a desired beam. Much development work has been directed to the design of the reflector and lens so as to produce a narrow beam and significant advances have been made in this regard.
One known light device is described in Russian patent application no. RF 98109712 “Headlight for Automobiles” (priority dated 19 May 1999 and published 27 Feb. 2000). That device includes a reflector, a refractor, and a light source. The reflector has a base surface of spherical, parabolic, elliptical or hyperbolic type and is equipped with convex or concave basic reflecting elements whose working surface is shaped as a Bezier surface or looks like a circle or an ellipse in the vertical and horizontal cross-sections. In addition, the basic reflecting elements are equipped with concentrating reflecting elements whose vertical dimension is less than or equal to that of the basic reflecting elements, and the horizontal dimension is less than or equal to that of the basic reflecting elements.
Another known light device is described in Russian patent no. RF 2115060 “Headlight for Transport Vehicles” (priority dated 16 Dec. 1993 and published 10 Jul. 1998). That headlight is a projection type headlight and includes a reflector, a light source, a screen and a lens. The reflector is a concave surface shaped as a paraboloid, the light source is located inside this reflector, and the lens is located so that its optical axis coincides with the reflector's optical axis, and its focal point coincides with the focal point of the same reflector.
A further known device is described in Russian patent no. RF 2149307 “Light Device” (priority dated 1 Dec. 1998 and published 20 May 2000. That device includes a light source, an ellipsoidal reflector, a lens projection system optically aligned with the ellipsoidal reflector, and a reflector-diaphragm located between the ellipsoidal reflector and the projection system. The light source is located in the ellipsoidal reflectors geometrical center, and the ellipsoidal reflector proper and the lens projection system are so arranged relative to each other that their focal points coincide.
Devices such as described in these patents typically have limited luminous flux intensity or optical density in the transmitted beam, e.g., because the direct association of the source with the reflector provides a beam diameter at least as great as that of the reflector, because the lens projection system provides a collimated or diverging beam or because the devices otherwise generally provide a beam that is not compressed along its axis.